[Bug 199727] CPU freezes in KVM guests during high IO load on host

[bugzilla-daemon@kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=199727

--- Comment #15 from Roland Kletzing (devzero@web.de) ---
yes, i was using cache=none and io_uring also caused issues. 

>aio=threads avoids softlockups because the preadv(2)/pwritev(2)/fdatasync(2)
> syscalls run in worker threads that don't take the QEMU global mutex. 
>Therefore vcpu threads can execute even when I/O is stuck in the kernel due to
>a lock.

yes, that was a long search/journey to get to this information/params....

regarding io_uring - after proxmox enabled it as default, it was taken back
again after some issues had been reported.

have look at:
https://github.com/proxmox/qemu-server/blob/master/debian/changelog

maybe it's not ready for primetime yet !?

-- Proxmox Support Team <support@proxmox.com>  Fri, 30 Jul 2021 16:53:44 +0200
qemu-server (7.0-11) bullseye; urgency=medium
<snip>
  * lvm: avoid the use of io_uring for now
<snip>
-- Proxmox Support Team <support@proxmox.com>  Fri, 23 Jul 2021 11:08:48 +0200
qemu-server (7.0-10) bullseye; urgency=medium
<snip>
  * avoid using io_uring for drives backed by LVM and configured for write-back
    or write-through cache
<snip>
 -- Proxmox Support Team <support@proxmox.com>  Mon, 05 Jul 2021 20:49:50 +0200
qemu-server (7.0-6) bullseye; urgency=medium
<snip>
  * For now do not use io_uring for drives backed by Ceph RBD, with KRBD and
    write-back or write-through cache enabled, as in that case some polling/IO
    may hang in QEMU 6.0.
<snip>

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